The invention relates to a device for measuring the temperature of a gas, in particular of air, which temperature is dependent on at least the flow velocity and humidity of the gas, comprising a housing having a wall displaying a heat-conducting and electrically-conducting material, which wall essentially separates the interior of the housing from the exterior environment, a thermocouple arranged inside the housing, and heating equipment arranged inside the housing.
It is generally known that the objectively measured temperature of a gas or gas mixture, such as, in particular, the air, does not always correspond to the subjectively xe2x80x9cfeltxe2x80x9d temperature. Factors such as, in particular, the gas velocity or wind velocity and the humidity influence the subjective sensation of the temperature.
A device of the type mentioned above is described in EP-A-0 214 294. In this known invention, a thermocouple is arranged inside the housing as the temperature sensor.
The object of the invention is to modify a device of the type mentioned in the introduction so that it operates in a more reliable manner.
This object is accomplished in a device of the type mentioned in the introduction by the fact that the end of one wire of the thermocouple is situated in contact with the inner side of the housing wall at a first location, the end of the other wire is situated in contact with the inner side of the housing wall at a second location, which is distanced from the first location, and the thermocouple forms a mean value from the temperature values measured at the two locations.
With the aid of the invention, more reliable measurement results are achieved than in the case of the prior art. For, although the housing wall consists of heat-conducting material, it is nevertheless possible that the housing wall does not exhibit a uniform temperature. That is to say, if the temperature is measured in only one location, then it can be affected by a singular defect, so that a falsely detected temperature is ascertained. Since according to the invention the temperature is measured by a thermocouple at two locations and automatically averaged, the device operates more reliably.
The invention is not suggested through the prior art. In the device according to U.S. Pat. No. 4,504,157, application is made of only a single temperature sensor, similarly in the device according to EP-A-0 214 294. To be sure, in the device according to DE-A-36 11 084 two temperature sensors are provided; however, only one temperature sensor is used for measuring the temperature of the housing wall, while the other temperature sensor is used merely as a thermostat for regulating the heating equipment.
In addition, the invention presents a simple and thus cost-effective structure, so that the use of the device according to the invention offers advantages precisely in cost-critical applications.
The arrangement according to the invention functions as follows. Through the heating equipment the interior of the housing is warmed, so that a certain temperature shows up on a temperature sensor arranged inside the housing. On the assumption of a temperature difference produced by the heating equipment with respect to the environmental temperature and held essentially constant, the temperature measured at the temperature sensor becomes so much the higher, the higher the environmental temperature outside the housing is, and so much the lower, the lower the environmental temperature is. In dependence on the wind velocity of the gas surrounding the housing, in particular the air, the housing wall is correspondingly cooled, since the wind, depending on its velocity, draws more or less energy and thus heat out of the interior of the housing through the housing wall designed so as to be heat conducting. In the same way the environmental humidity influences the temperature inside the housing. Since, that is to say, the moisture precipitating on the outside of the housing wall strives to evaporate, evaporation energy is necessary, which energy is drawn from the interior of the housing through the heat-conducting housing wall. Both of these effects, which can occur in a cumulative manner, act to cause a reduction of the heat measured in the interior of the housing by the thermocouple, so that the thermocouple is directly subjected to these influences and thus gives a temperature value that corresponds in essence to the xe2x80x9cfeltxe2x80x9d temperature and can be appropriately processed in a possibly downstream-connected evaluation unit. Thus it is possible to determine simultaneously with the temperature the most important parameters influencing the latter, such as wind velocity and humidity, and to generate for the xe2x80x9cfeltxe2x80x9d temperature only a single relevant signal, which can be processed and displayed in a downstream-connected evaluation unit.
Preferably, the outside of the wall of the housing in covered in the main with a hydrophilic layer of moisture-receptive material, in order to be capable of more effectively storing moisture precipitating on the outside of the housing wall. This embodiment in particular is based on the idea of reproducing the housing wall of the human skin with respect to sensitivity to temperature and the parameters influencing the latter, particularly humidity, using simple means and to the extent possible. In order to enable the reception of an appropriate degree of moisture for the measurement, the hydrophilic layer should consist of textile material, in particular felt material. The material here should appropriately be chosen so that it imitates the human skin with respect to its heat- and moisture-absorbing characteristics.
Since the device according to the invention is at least intended, among other things, for the measurement of the temperature as felt on the human skin, the heating equipment can, for example, radiate heat the temperature of which approximately corresponds to the average human body temperature. Accordingly, the heating equipment could be appropriately controlled or set so that, due to the heat generated inside the housing by the heating equipment, the temperature sensor measures a temperature value that approximately corresponds to the average human body temperature when ideally neither an influencing by the environmental temperature outside the housing (corresponding to the state of an ideal insulating of the housing with respect to the environment) nor an influencing by the velocity (wind strength) and humidity of a gas surrounding the housing, in particular the air, (thus, wind velocity=0 and humidity=0%) predominates. In this respect, such a temperature value is a matter of a reference value, which specifies the state of the measurement device according to the invention in which it is completely uninfluenced by the environment in an ideal manner; thus, in this state the parameters influencing the measured temperature are for practical purposes excluded. Alternatively, it is also conceivable to set the heating equipment in a situation in which the (objectively) measured temperature corresponds to the (subjectively) felt temperature; to this end, there are fixed criteria, to which one must then pay attention. For the rest, it goes without saying that, depending on the desired application case, a reference temperature other than the value of the average human body temperature can also be chosen.
In order to avoid a point-focused heating of the housing wall, but rather to realize the most uniform possible heat distribution inside the housing, the heating equipment should be arranged at a distance from the wall of the housing.
Preferably, the housing should be filled with a fill material, consisting in particular of casting material. In this way it is possible to improve the heat-transfer or heat-conducting characteristics inside the housing, or, as the case may be, to adapt to the desired application case, the fill material with the desired heat-conducting characteristics being chosen.
The housing can be designed as a pipe, in particular a cylindrical pipe, whereby are achieved, first, an especially high degree of mechanical strength, and second, an especially favorable relation between surface and interior volume.
The temperature sensor normally generates signals and delivers these to an evaluation unit for evaluation and display of the measured temperature value.